Pipes used for hot water in houses are generally made of iron, usually buried in walls. But iron pipes are extremely liable to get rusted, unable to last long, so stainless pipes has gradually taken place of them. Nevertheless, there is a problem for the stainless pipes, that is, expansion caused by high temperature of hot water. The traditional method for joining pipes uses pipe fittings provided with male and female threads, which are usually a little inclined, not completely fitting with the threads on the ends of pipes. Besides, the thickness of the ends of pipes can become thinner because of the threads cut therein so that the joined sections can often brake owing to the expansion caused by hot water
This applicant has often experienced this shortcoming in many years' work, and filed and acquired an American patent, Ser. No. 4,792,160, which furnishes a joining structure suitable for small diameter metal pipes and those to be hidden in walls, but not suitable for those of large diameter and those exposed.